Dual brake apparatus for automobiles



E. G. CARROLL DUAL BRAKE APPARATUS FOR AUTOMOBILES Oct. 30, 1934.

Original Filed Aug. 20, 1927 INVENTOR. fugefle 6'. Camell. BY 6 rfi044.. ATTO N22 meted 0a. 30, 1934 UNITED STATES DUAL BRAKE APPARATUSFort AUTOMOBILES Eugene G. Carroll, Los Angeles, Calif., assignor,

by mesne assignments, to Bendix Brake Gompany, South Bend, Ind., acorporation of Illi-.

nois

Original application August 20, 1927, Serial No. 214,330. Divided andthis application February 5, 1929, Serial No. 337,564. Renewed September17 Claims. (Cl. 54.6)

This invention relates to a fluid brake apparatus and is intendedespecially for use on automobiles. This application is a division of mycopending application Serial No. 214,330, Patent No.

1,770,064, granted July 8, 1930.

In operation of automobile brakes of the fourwheel type, it has becomerecognized as bad practice to have the front wheels braked with greaterforce than the rear wheels. In fact, the braking action should begreatest on the rear wheels. One of the objects of this invention is toprovide an apparatus which will automatically insure that the brakingeffect on the front wheels will be less than that on the rear wheels;also to construct the apparatus in such a way that in case the brakingapparatus for the rear wheels, or for the front wheels, should becomeinactive then the braking apparatus for the other wheels -will continueto function effectively.

Accidents have occurred in using fluid operated brakes due to the factthat one of the forward brakes -will operate and the other forward brakefails to operate, thereby tending to steer the car to one side. One ofthe objects of this invention is to provide an apparatus in which thetwo forward brakes receive their pressure from the same source, so thatif the pressure in one of the forward brakes fails, the pressure in theother forward brake will also fail.

In other words, according to my invention, I provide a dual system forthe rear wheel brake cylinders and for the front wheel brake cylinders,connected up in such a way that there is a regulating pressureconnection between the two apparatuses preventing the application of toogreat power to the front wheels, but enabling it to continue to functionproperly in case the front wheel braking apparatus gets out of order,and vice versa; and this is accomplished automatically and without anyadjustment vor attention being necessary from the driver of the car.

Further objects hereinafter.

The invention consists in the novel parts and combination of parts to bedescribed hereinafter, all of which contribute to produce an eflicientdual brake apparatus for automobiles.

A preferred embodiment of the invention is described in the followingspecification, while the broad scope of the invention is pointed out inthe appended claims.

In the drawing: Figure 1 is a plan showing a twin of the invention willappear cylinder conthe rear section taken on the line 2-2 of Figure 1and further il1ustrating details of the apparatus. This view alsoillustrates a dual reservoir which may be used with this type of twincylinder.

Figure 3 is a horizontal section taken on the line 33' of Figure 2.

In practicing the invention, I provide cylinder means, including meansfor developing pressure therein in the operating fluid.

In order to provide for inhibiting the remaining forward'brake' fromoperating in case the other forward brake fails to operate, I provide apipe leading from the cylinder means, with a branch corresponding toeach forward wheel. For a similar purpose I provide another pipe leadingfrom the cylinder means, having a branch corresponding to each of therear wheels.

In order to provide for developing a slightly reduced pressure in theforward brakes, so that they will be applied with less force than therear brakes, I employ a "forward pressure chamber and a rear pressurechamber, the former of which supplies the fluid under' pressure to theforward brakes, and the latter of which supplies the fluid underpressure to the rear brakes.

I provide automatic means for maintaining a certain regulation orrelation of the pressures of these two pressure chambers, and this meansis preferably constructed so that the apparatus will continue theoperation of either the forward set construction -for attaining theseefiects.

I. provide cylinder means 1, preferably of twin type so that twocylinders 2 and 3 are provided with parallel axes. If desired, thesecylinders may be cast in a block. I prefer to construct each of thesecylinders, 2 and 3, with a forward bore 4 of reduced diameter, and arear bore 5 of slightly larger diameter, and connect the two bores bymeans of by-pass ports 6 and '1 formed in the cylinder walls. (SeeFigure 2.) These bores are supplied with a fluid, preferably a'liquid,which I prefer to carry in a twin type reservoir 8 having two chambers 9and 10 alongside of each other and separated by a dividing wall 11. Thechamber 9 is connected by a pipe connection 12 with a'small chamber 13formed at the junction point of the ports 6 and 7. In a. similar way thereservoir 10 is connected by a pipe connection indicated at 14 with asimilar chamber 13 of the other twin cylinder. (See Figure 2.)

The brake pedal that applies the brakes exerts thrust in a rod 15 thatis attached to a cross-head 16, and this cross-head is attached topiston rods 17 that extend into the two twin cylinders 2 and 3, saidrods being located on the axes of the cylinders. The piston rods 17carry pistons 18 and 19, the former of which is located in therelatively large bore 5 andthe latter of which is located in the bore 4of relatively small diameter.

The cylinders 4 communicate with an equalizing chamber 20 which may beformed in a crosscylinder 21 cast en bloc with the twin cylinders 2 and3, and the ends of this chamber communicate respectively with the twincylinders 2 and 3.

I provide means for regulating the relative pressure in the two ends ofthe pressure chamber 20. For this purpose I prefer to employ a movablepiston 22 in the bore of the cylinder 21 which divides the chamber 20into two separated chambers, namely, a chamber 23 which I call a forwardchamber, and a chamber 24 which I call a rear chamber. The chamber 23 isconnected by a pipe F with branches 25 and 26 that connect respectivelyto the two forward brake cylinders. A similar pipe connection, R, isconnected to the chamber 24, and this pipe has branches 27 and 28 thatconnect respectively to the rear brake cylinders. The piston 22 isnormally held by a spring in an extreme position. This spring is mountedso that it urges the piston 22 in a direction to diminish the volume inthe chamber 23. This spring has little force and is a return spring ofjust sumcient strength to overcome the friction of the piston 22. Withthis arrangement it will be evident that if the pressure in the chamber23 (communicating with the front'wheels) tends to increase, thispressure will move the piston 22 toward chamber 24, thereby enlargingthe chamber 23, and this will automatically reduce the pressure of theliquid or fluid serving the forward brakes.

In the present instance the spring is in the form of a coil spring 29located in the chamber 24, and this spring normally holds the piston 22over against a plug 30 screwed into the opposite end of thecross-cylinder 21.

The piston 22 may be of any suitable construction. In the presentinstance it is constructed of two separated heads 31 and 32 with a body33 located between them. The inner ends of the heads 31 and 32 havetapered or conical integral collars 34, which exert their pressureagainst cup leathers 35,'which operate as packing to prevent leakagebetween the two chambers 23 and 24.

The pipes F and R. are connected to their corresponding ends of thecylinder 21 preferably as indicated in Figure 2, each pipe terminatingin a connection 36 screwed into a boss located opposite the inner endsof the bores 4 and communicating with a small chamber 37 in the boss,which connects by ports 38 and 39 with the bore 4 and the correspondingchamber of the cross-cylinder.

I prefer to provide an air chamber 40 in the reservoir 8, which isconstructed to retain air under pressure. This pressure may bemaintained at any desired point, for example, five or six pounds persquare inch above atmospheric pressure. For this purpose the reservoir 8is preferably provided with an air-tight cover 41 which is preferablyprovided with an air inlet 42 and a check-valve 43 opening inwardly andnormally held closed by a light coil spring 44. With this constructionit will be evident that in case the air pressure in the air chamber 40ever drops below atmospheric pressure, the check-valve 43 would openautomatically and admit more air.

The ports I admit fluid into the forward bores 4 just forward of theirpistons 19. In the operation of the brake, when the cross-head 16 isactuated, the fluid displaced by each of the larger pistons 18 flowsthrough the port 6 into the corresponding small chamber 13, raising thelevel of the liquid in the chambers 9 and 10 of the reservoir 8 andslightly increasing the pressure, both hydrostatic and pneumatic, in thesystem. This increase of pressure is, of course, vof a differentialnature, because each forwardly moving small piston 19 is increasing thevolume of its respective chamber 5. However, there is an increase ofpressure developed which is communicated to the forward bore 4 until theport '7 closes. ably higher pressure is immediately developed in theforward bores 4, which are cut oil from communication with theirreservoirs. This applies the braking pressure through the pipes F and Rto the forward and rear brake cylinders.

If there is any tendency for the pressure in the chamber 23 to becomehigher than its proper working pressure relative to the pressure inchamber 24, then a displacement of the piston 22 would take place in adirection to compress the spring 29 and enlarge the chamber 23. Thiswould automatically reduce the pressure in the liquid serving theforward brakes. This is advantageous because it is desirable to havesomewhat less braking force applied to the forward wheels.

If desired, a pressure gauge can be provided on the cover 41 forindicating the pressure existing in the brake apparatus. I

If one of the forward brakes should leak so that the brake would not beapplied, the reduction in pressure incidental to the leak would becommunicated through its branch pipe to the other forward brake, so thatthe pressure in the two forward brake cylinders is always equalized.This prevents either forward brake being applied with greater force thanthe other. And, if one forward brake fails by loss of pressure, so willthe other. This is also true of the rear brakes, but the forward set ofbrakes can become inoperative without affecting the operativeness of therear brakes. In case the rear brakes failed, the piston 22 wouldmove-over against the other end of chamber 24, (see Figure'3) therebydecreasing. the pressure in the system serving the forward brakes. Adecreased braking effect in the forward wheels would result, and this isdesirable when they are the only brakes operating on the car.

This apparatus automatically develops working pressure in the airchambers. This occurs by reason of the fact that when first put into usethe return movement of the pistons 18 will develop a partial vacuum inthe chambers 5. This will cause atmospheric air to leak in. In this waythe pressure will be built up.

The surfaces of contact between the plug 30 and the head 32 are rough.unfinished faces, that is to say, they are not machined faces, andconsequently when the head 32 seats against theplug 30,'as illustratedin Figure 3, the contact between these two parts is limited to a pointor sev- As soon as this port closes, a considervolume of the chamber 24,the head 31 shoulderal points so that there is substantially no area cutoff from the pressure in the chamber 23 against the seating face of thehead 32. For this reason it is not possible for the head 32 to becomeset permanently against the plug 30. Furthermore, when the piston 22 ismoved by the pressure in the chamber 23 in a direction to reduce nevermove far enough to seat against the adjacent head of the cylinder. Thechamber 24 is long enough, measured along the axis of the piston, toprevent this. The safe length of the chamber as regards this point isdetermined by the capacity of the pipes and brake cylinders. In anycase, the length of this chamber should be sufficient to prevent such aseating of the head 31 in its movement that compresses the spring 29.

side of the same receiving the operating fluid, and

means for normally holding the equalizing piston yieldingly in anextreme position with respect to one of said chambers, a connection fromone of said chambers to the forward braking cylinders and aconnectionirom the other chamber to the rear braking cylinders.

2, In a four-wheel fluid brake apparatus for automobiles, thecombination of cylinder means including means for developing pressuretherein in the operating fluid, a chamber receiving fluid from thecylinder means and corresponding to the forward wheels, another chamberreceiving fluid from the cylinder means and corresponding to the rearwheels, means movably mounted in-the space between the chambers forconstantly separating the chambers from each other and preventing thepassage of liquid from one to the other for regulating the relativepressures in said chambers, a pipe connection connecting the first ofsaid chambers with the forward wheels, and a pipe connection connectingthe other of said chambers with the rear wheels.

3. In a four-wheel fluid brake apparatus for automobiles, thecombination of cylinder means, including means for developing pressuretherein] in the operating fluid, a chamber receiving fluid from thecylinder means and corresponding to the forward wheels, another chamberreceiving fluid from the cylinder means and corresponding to the rearwheels, a movable piston separating the said chambers from each other, aspring urging the piston toward the chamber corresponding to the forwardwheels and operating to yield if the pressure tends to rise above apredetermined brake pressure in the forward chamber, thereby enlargingthe "forward chamber and preventing the rise of the pressure in theforward chamber above the predetermined brake pressure.

4. In a four-wheel fluid brake apparatus for automobiles, thecombination of cylinder means including means for developing pressuretherein in the operating fluid, a "forward chamber receiving fluid fromthe cylinder means and corresponding to the forward wheels, a rearchamber correspondingto the rear wheels and receiving fluid from thesaid cylinder means, a movable piston separating the said chambers and aspring urging the piston in one direction and yielding to permitenlargement of the forward chamber. a

5. In a four-wheel fluid brake apparatus for automobiles, thecombination of a master cylinder of twin type having two twin cylindersside by side, each of said cylinders having a chamber with itscorresponding piston means, means for advancing both of said pistonmeans simultaneously, a forward chamber adjacent to the chamber of oneof said twin cylinders, with a connecting port, receiving fluid underpressure from one of said twin cylinders, a rear chamber adjacent theother twin cylinder with a connecting port receiving fluid underpressure from the other of said twin cylinders, a pipe connection fromthe forward" chamber to the forward wheels, a pipe connection. from therear chamher to the rear wheels, and means for controlling the relativepressures in the two chambers.

6. In a fluid brake system for automobiles, the combination of aplurality of master cylinders, means for developing fluid pressures insaid cylinders, a connection between said cylinders, and meanscomprising a floating fluid tight piston in said connection forconstantly separating the portions of said connection-which lead to saidcylinders respectively.

7. In a fluid brake system for operating fluid motors associated withthe brakes, a master cylinder means, movable means for dividing saidmaster cylinder means into a pair of compartments and preventing theflow of fluid from one compartment to the other, a piston in eachcompartment, connections between one of said com- I partments and one ofsaid fluid motors, connections between another of said compartments andanother of said fluid motors, means for normally maintainingsuperatmospheric pressure in said system, means cooperating with saidpistons and with said movable means for producing substantially equalpressures in said compartments so long as the pressures remainsuperatmospheric in both of said compartments, and means for limitingthe movement of said dividing means to prevent dissipation of pressuresin one of said compartments consequent upon dissipation of pressure inthe other compartment.

8. In hydraulic brake apparatus, forward .brakes and rear brakes, amaster cylinder means having a plurality of compartments, means in eachof said compartments for developing hydraulic pressure therein, fluidpressure connections between one of said compartments and said saidfirst named cylinders, a fluid tight floating piston in said transversecylinder, at fluid connection between one of said parallel cylinders andone of said brakes, and a fluid connection between the other ,of saidparallel cylinders and another of said brakes.

10. In hydraulic brake apparatus, a master cylinder, a. wheel cylinder,fluid connections between said master cylinder and said wheel cylinder,a supply reservoir having an opening to the atmosphere in the upper partthereof and having a check valve therein whereby air may be drawn intosaid reservoir and whereby fluid may be prevented from passing out ofsaid reservoir, said cylinder having a piston therein adapted to bereciprocated for supplying operating pressure to said wheel cylinder,and having a second different sized piston positioned rearward of saidfirst named piston also adapted to be reciprocated and connectionsbetween said master cylinder and said reservoir leading to said cylinderat a point between the pistons whereby the pressure in said reservoir isalternately raised and lowered by reason of the reciprocation of saidpistons.

11. A fluid pressure braking means involving independent hydraulicsystems, manual means for creating braking pressure in said systems, anda balancing device intermediate the systems and including a floatingpiston serving to prevent fluid interchange betweenthe systems, themovement of the piston in one direction under a limited excess pressurein onesystem serving in such movement to tend to balance the pressuresin the respective systems.

12. A fluid pressure braking means involving independent hydraulicsystems, manual means for creating braking pressure in said systems, anda balancing device intermediate the systems and including a floatingpiston responsive to the pressure of each system and serving to preventfluid interchange between the systems, the movement of the piston in onedirection under a limited excess pressure in one system serving in suchmovement to tend to balance the pressures in the respective systems.

13. A fluid pressure braking means including independent hydraulic brakecontrolling systems, a balancing device for equalizing pressure betweenthe systems including a floating piston responsive to an excess pressurein one of the systems and moving under such excess pressure to increasethe pressure in the other system and reduce the pressure in the flrstmen- 'tioned' system to a pressure balancing point,

and means for limiting pressure responsive movement of the piston ineither direction to prevent pressure exchange between the systems beyonda predetermined limitof pressure variation in the respective systems.

14. A fluid pressure braking means including independent brakecontrolling hydraulic systems,

a pressure balancing means between the systems including a cylinderclosed at the respective ends, a piston operative within the cylinderand normally defining chambers beyond each end of the piston, eachpressure system including one of said chambers, the piston floating withrespect to the chambers and responsive to variation in pressure in thechambers, said piston further preventing fluid exchange between thechambers, said piston under variation in pressure in one of the chambersand thereby in the system of which said chamber forms a part moving toreduce the normal volume of the other chamber to thereby increase thepressurein such other chamber and in the system in which said otherchamber forms a part.

15. A fluid pressure braking 'means including independent brakecontrolling hydraulic systems, a pressure balancing means between thesystems including a cylinder closed at the respective ends, a pistonoperative within the cylinder and normally defining chambers beyond eachend of the piston, each pressure system including one of said chambers,the piston floating with respect to the chambers and responsive tovariation in pressure in the chambers, said piston further preventingfluid exchange between the chambers, said piston under variation inpressure in one of the chambers and thereby in the system of which saidchamber forms a part moving to reduce the normal volume of the otherchamber to thereby increase the pressure in such other chamber and inthe system in which said other chamber forms a part, and means forlimiting pressure responsive movement of the piston in either direction.

16. In a hydraulic braking system, in combination a plurality of fluidoperated brake mechanisms, a master cylinder and a piston therein forproducing fluid pressure associated with each of the brake mechanisms, acylinder and a piston therein common to said brake mechanisms and mastercylinders, packing cups for said piston, heads for said piston, meansengageable with said heads for limiting the range of movement of saidpiston, a coil spring for holding said cups in a manner to preventleakage of fluid past said piston and for normally holding one of saidheads spaced from one of said limiting means to permit a predeterminedmovement of said piston by a difierential in pressure in said brakemechanisms due to variations in adjustment of the brake mechanisms tolimit the pressure of one of said master cylinders.

1'7. In a hydraulic braking system, in combination a plurality of fluidoperated brake mechanisms, a master cylinder and a piston therein forproducing fluid pressure associated with each of the brake mechanisms, acommon cylinder and a piston therein interposed between said mastercylinders and brake mechanisms, packing cups seated on opposite faces ofsaid piston, a head for said piston, means engageable with said head forlimiting the range of movement of said piston, means yieldingly urgingsaid piston to a position such that the piston may be moved in onedirection by a differential in pressures in said brake mechanisms due tovariations in adjustment of the brakes of said brake mechanisms to limitthe pressure of one of said master cylinders relative to the other.

EUGENE G. CARROLL.

